1. Technical Field
The disclosure relates signal transmitting circuit of driving signal for driving a light source, and more particularly, to a signal transmitting circuit for cutting off the driving signal for driving a designated light source, and a display module and an electronic apparatus equipped with the signal transmitting circuit.
2. Related Art
The Night Vision Imaging System (NVIS) generates a relatively large gain for a red light. When a user observes a display device through the NVIS, the NVIS will generate relatively large gain for red light and infrared light emitted by the display device. Due to the aforementioned reason, the images displayed by the display device will have a high brightness and low contrast in the NVIS, and it is difficult for the user to clearly observe the display device through the NVIS.
In practice, the approach for observing display device through the NVIS is to attach an optical filter on the display panel of the display device to cut off light other than 400 nm-600 nm wavelength light. Through the optical filter, the red light emitted by the display panel is cut off as possible. However, the cost of the optic filter is high. Moreover, if an optical filter is attached to the display panel of a touch-control display device, the optic filter interferes with the operation of a touch-control interface. Therefore, the aforementioned approach is not suitable for a display device with touch-control interface.
The display device displays variant colors by mixing red, green, and blue colors of red, green, and blue pixel cells. When observing the display device through the NVIS, another approach is to cut off red light from red pixel cells to prevent the display device from emitting red light and infrared light, and than it is possible for the user to clearly observe the images on the display device through the NVIS.
Different from a common desktop computer in which the computer host and display device are separated, in a portable electronic apparatus, a laptop computer, or an all-in-one computer, the display signal generated by the main electronic circuit is transmitted to a driving circuit of a display module through Low-Voltage Differential Signaling (LVDS) mechanism performed by a Low-Voltage Differential Signaling transmitter (LVDS transmitter).
Please refer to FIG. 1; an LVDS transmitter in the art includes an input differential signaling driver 1 and an output differential amplifier 2. The input differential signaling driver 1 is provided for receiving a display signal S-in and generating an inverting signal and a non-inverting signal according to the display signal S-in. Then, the input differential signaling driver 1 transmits the inverting signal and the non-inverting signal to the output differential amplifier 2 through signal lines 3, 4. The output differential amplifier 2 determines a driving signal S-out for driving a designated light source to be high-voltage-level or low-voltage level according to the voltage-level difference between the inverting signal and the non-inverting signal, and then transmits the driving signal S-out to the driving circuit of the display panel.
Please refer to FIG. 2. When observing display device through the NVIS, the driving signal for driving the display device to emit red light has to be cut off. The approach for cutting off red light is to dispose two change-over switches 5, 6 in the LVDS transmitter 1. When red light has to be cut off, the two change-over switches 5, 6 respectively enable two receiving points of the output differential amplifier 2 to be electrically grounded, therefore the voltage-level difference between two receiving points of the output differential amplifier 2 remain at zero. Theoretically, the outputting points of the output differential amplifier 2 will remain at low-voltage level instead of output the driving signal for driving designated light source corresponding to red light. Since the driving signal for driving designated light source corresponding to red light is cut off, the display device stop emitting red light.
In fact, even though two receiving points of the output differential amplifier 2 are electrically grounded, some external facts such as Electromagnetic interference (EMI) may generate high voltage pulse two any one of the two receiving points of the output differential amplifier 2. Such high voltage pulse cause that the voltage-level difference between two receiving points of the output differential amplifier 2 can not continuously remain at zero when the two receiving points are electrically grounded. As a result, the output differential amplifier 3 occasionally output the driving signal and the display device is occasionally or continuously driven to emit red light.